1. Field of the Invention
The present invention relates to an image decoding device in which image data is output by switching a dot clock, an image decoding method, and a storage medium and an integrated circuit thereof.
2. Description of Related Art
Currently, in the MPEG standard, a frame rate, which is the frequency for displaying an image of a frame, such as 30 Hz/29.97 Hz, 60 Hz/59.94 Hz, or the like is permitted in the preparation of stream data having a difference in the thousandths. For example, when the frame rate included in the stream data is 29.97 Hz, in a television having an image decoding device which is set to a frame rate of 29.97 Hz, the image is displayed according to this frame rate.
When stream data having the frame rate of 30 Hz is input into the image decoding device which is set to the frame rate of 29.97 Hz or when stream data having the frame rate of 29.97 Hz is input into the image decoding device which is set to the frame rate of 30 Hz display frequency errors accumulate over time because the frequencies displaying an image differ from each other in the thousandths. In conventional image decoding devices, a part of the stream data which is input into the image decoding device is deleted or a repeat, a skip, and the like, of the image data to be displayed is performed in order to resolve these problems.
However, in conventional image decoding devices, as mentioned above, if the stream data having a frame rate which differs from the frame rate set in the image decoding device is input into the image decoding device, a part of the stream data is deleted or a repeat, a skip, and the like, of the image data to be displayed is performed therefore, the transmitted image cannot be accurately reproduced.
In light of the above problem, an object of the present invention is to provide an image decoding device which smoothly displays images even if stream data having two or more different frame rates is input into the image decoding device.
To achieve the above object, the present invention provides an image decoding device in which encoded animation data is decoded and pictures are output in the order of displaying each picture according to decoded animation data, comprising: a frame rate information extracting means which extracts frame rate information corresponding to each picture contained in a stream from an input stream; a storing means which temporarily stores the frame rate information extracted by the frame rate information extracting means; a dot clock output means which outputs a dot clock in order to display images; and a control means which switches the frequency of the dot clock output by the dot clock output means when the output frame rate information stored in the storing means is read in the order of displaying each picture and when the dot clock of the arrayed frame rate information changes.
Furthermore, in the above image decoding device, the control means may switch the frequency of the dot clock output by the dot clock output means when the read frame rate information and the frame rate information which is read just prior to the read frame rate information are compared with each other and are found to be different.
Moreover, in the above image decoding device, the control means may switch the dot clock when a picture set by the frame rate information which differs from the just prior frame rate information is displayed.
The present invention further provides an integrated circuit device comprising an image decoding circuit which decodes encoded animation data and outputs pictures in the order of displaying each picture according to the encoded animation data, comprising: a frame rate information extracting means which extracts frame rate information corresponding to each picture contained in a stream from an input stream; a storing means which temporarily stores the frame rate information extracted by the frame rate information extracting means; a dot clock output means which outputs a dot clock in order to display images; and a control means which switches the frequency of the dot clock output by the dot clock output means when the output frame rate information stored in the storing means is read in the order of displaying each picture and when the dot clock of the arrayed frame rate information changes.
Furthermore, in the above integrated circuit device, the control means may switch the frequency of the dot clock output by the dot clock output means when the read frame rate information and the frame rate information which is read just prior to the read frame rate information are compared with each other and are found to be different.
Moreover, in the above integrated circuit device, the control means may switch the dot clock when a picture set by the frame rate information which differs from the just prior frame rate information is displayed.
The present invention further provides an image decoding method comprising an image decoding system which decodes encoded animation data and outputs pictures in the order of displaying each picture according to the encoded animation data, comprising the steps of: a frame rate information extracting step which extracts frame rate information corresponding to each picture contained in a stream from an input stream; a storing step which temporarily stores the frame rate information extracted by the frame rate information extracting step; a dot clock output step which outputs a dot clock in order to display images; and a control step which switches the frequency of the dot clock output by the dot clock output step when the output frame rate information stored in the storing step is read in the order of displaying each picture and when the dot clock of the arrayed frame rate information changes.
Furthermore, in the above image decoding method, the control step may switch the frequency of the dot clock output by the dot clock output step when the read frame rate information and the frame rate information which is read just prior to the read frame rate information are compared with each other and are found to be different.
Moreover, in the above image decoding method, the control step may switch the dot clock when a picture set by the frame rate information which differs from the just prior frame rate information is displayed.
The present invention further provides a storage medium, which is readable by a computer, storing an image decoding program for making a computer execute a decoding operation on encoded animation data and an outputting operation on pictures in the order of displaying each picture according to the encoded animation data, the image decoding program comprising the steps of: a frame rate information extracting step which extracts frame rate information corresponding to each picture contained in a stream from an input stream; a storing step which temporarily stores the frame rate information extracted by the frame rate information extracting step; a dot clock output step which outputs a dot clock in order to display images; and a control step which switches the frequency of the dot clock output by the dot clock output step when the output frame rate information stored in the storing step is read in the order of displaying each picture and when the dot clock of the arrayed frame rate information changes.
Furthermore, in the above storage medium, the control step may switch the frequency of the dot clock output by the dot clock output step when the read frame rate information and the frame rate information which is read just prior to the read frame rate information are compared with each other and are found to be different.
Moreover, in the above storage medium, the control step may switch the dot clock when a picture set by the frame rate information which differs from the just prior frame rate information is displayed.
As mentioned above, according to the present invention, since the frequency of the dot clock for displaying the image is switched when the frame rate information comprised in the stream corresponding to each picture is extracted from the input stream, the extracted frame rate information is temporarily stored, the output frame rate information which is stored in the order of displaying the picture information is arrayed, and the dot clock of the arrayed frame rate changes, even if stream data in which there are frame rates each having different frequencies, is input into the image decoding device, an effect can be obtained wherein images are smoothly displayed.
Furthermore, according to the present invention, since the dot clock is switched when pictures are displayed wherein the frame rate information which differs from the previous frame rate information is set, an effect can be obtained wherein the output image data is accurately reproduced.